The present invention relates to a radio communication system which performs radio communication by transmitting and receiving radio carrier waves.
A conventional radio relay system which is one example of such a radio communication system is shown in FIGS. 10 and 11.
FIG. 10 is a block diagram showing a radio relay system employed, for instance, for mobile telephone devices. Reference may be made, for instance, to the publication "Mobile Communication--Theory and Principle", pp. 96 to 99, FIGS. 5.1, 5.2 and 5.3 published by the Electronic Communication Society. FIG. 11 is an explanatory diagram showing the frequency bands of radio carrier waves used in the radio relay system.
In FIG. 10, reference numeral 1 designates a radio relay device A which performs communication with a mobile communication device A 2; 3, a radio relay device B which perform communication with a mobile communication device B 4; and 5, a cable assembly connected between the radio relay device A 1 and the radio relay device B 3.
Further in FIG. 10, reference numeral 6 designates an antenna A for transmitting and receiving radio carrier waves; 7, a signal receiver A for receiving radio carrier waves through the antenna A 6; 8, a signal transmitter A for transmitting radio carrier waves through the antenna A 6; 9, an antenna coupler A through which radio carrier waves received by the antenna A are applied to the signal receiver A 7 and through which radio carrier wave are applied to the antenna 6 by the signal transmitter A 8; 10, a synthesizer the oscillation frequency of which determines the operating frequency of the signal receiver A 7 and the signal transmitter A 8; and 11, a control circuit A for controlling the operations of the signal receiver A 7, the signal transmitter A 8, and the synthesizer A 9. The arrangement of the radio relay device B 3 is similar to that of the radio relay device A 1 described above. That is, reference numeral 12 designates an antenna B for the relay device 3; 13, a signal receiver B; 14, a signal transmitter B; 15, an antenna coupler; 16, a synthesizer B; and 17, a control circuit B. The cable assembly 5 includes: a cable 5a through which radio carriers waves received by the signal receiver A 7 are transmitted to the signal transmitter B 14; a cable 5b through which radio carrier waves received by the signal receiver B 13 are applied to the signal transmitter A 8; and a cable 5c through which the control circuit A 11 and the control circuit B 17 are connected to each other to transmit various data between them.
It is assumed that a frequency f.sub.RX1 is transmitted by the mobile communication device A 2 and received by the radio relay device A 1, and a frequency f.sub.TX1 is transmitted to the mobile communication device A 2 by the radio communication device A 1. Furthermore, it is assumed that a frequency f.sub.RX2 is transmitted by the mobile communication device B 4 and received by the radio relay device B 3, and a frequency f.sub.TX2 is transmitted to the mobile communication device B 4 by the radio relay device B 3. The frequencies f.sub.TX1 and f.sub.TX2 are close to each other, and the frequencies f.sub.RX1 and f.sub.RX2 are also close to each other. And the frequency band covering the frequencies f.sub.TX1 and f.sub.TX2 and the frequency band covering the frequencies f.sub.RX1 and f.sub.RX2 are sufficiently spaced away from each other, so as to prevent the mutual interference between the transmitting radio carrier wave and the receiving radio carrier wave.
The operation of the radio relay system thus arranged will be described.
First, a signal transmission will be described in which radio carrier wave is transmitted from the mobile communication device A 2 through the radio relay device A 1 and the radio relay device B 3 to the mobile communication device B 4. The radio carrier wave having the frequency f.sub.RX1 transmitted by the mobile communication device A 2 is received by the antenna A 6, and applied through the antenna coupler A 9 to the signal receiver A 7, where it is detected. The output signal of the signal receiver A 7 is applied through the cable 5a, as a signal reception base band signal, to the signal transmitter A 8. The signal reception base band signal is modulated by the signal transmitter B 14 into the radio carrier wave having the frequency f.sub.TX2, which is transmitted through the antenna coupler B 15 and the antenna B 12 to the mobile communication device B 4.
Next, a signal transmission opposite to the above-described signal transmission will be described in which a radio carrier wave is transmitted from the mobile communication device B 4 through the radio relay device B 3 and the radio relay device A 1 to the mobile communication device A 2. Similarly as in the above-described signal transmission, the radio carrier wave having the frequency f.sub.RX2 transmitted by the mobile communication device B 4 is received by the antenna B 12. The radio carrier wave thus received is transmitted through the antenna coupler B 15, the signal receiver B 13, the cable 5b, the signal transmitter A 8, the antenna coupler A 9 and the antenna A 6, as the radio carrier wave having the frequency f.sub.TX1, to the mobile communication A 2.
Now, a conventional cordless telephone system will be described which is another example of the radio communication system.
FIG. 12 is a block diagram showing the arrangement of the conventional cordless telephone system which is disclosed, for instance, by a paper "New Cordless Telephone", the publication "Shisetsu (Facilities)" 36, No. 3, 1979, pp. 134 to 141 published by the Electrical Communication Society. In FIG. 12, parts corresponding functionally to those which have been already described with reference to FIG. 10 are therefore designated by the same reference numerals or characters. Further in FIG. 12, reference numeral 35 designates a master telephone unit; 37, a slave telephone unit which performs communication through the antenna A 6 with the master telephone unit 35; and 70, a control/interface circuit for controlling the signal receiver A 7, the signal transmitter A 8 and the synthesizer A. The control/interface circuit 70 is connected to a telephone line 39 for signal transmission and reception.
The operation of the cordless telephone system thus organized will be described.
When the master telephone unit 35 receives an incoming calling signal through the telephone line 39 from outside, the control/interface circuit 70 causes the signal transmitter A to transmit a particular calling signal through the antenna A 6 in the air to the slave telephone unit A 37. Upon reception of the particular calling signal, the slave telephone unit is placed in communication state with the master telephone unit. The particular calling signal transmitted by the master telephone unit includes a registered ID (identification) number, so as to call the slave telephone unit corresponding to the ID number.
In the case when the slave telephone unit A 37 to call an external telephone unit, a calling signal outputted by the slave telephone unit is applied through the antenna A 6 and the antenna coupler A 9 to the signal receiver A 7, where it is detected. The output signal of the signal receiver is applied, as a calling signal, to the telephone line 39 through the control/interface circuit 70. The calling signal also includes a registered ID number; that is, the master telephone unit 35 receives only the calling signal including the registered ID number.
In general, such incoming calling signals, or outgoing calling signals, are received only by the master telephone unit and the slave telephone unit which have the registered ID numbers, and the master telephone unit is installed indoors.
Now, a conventional base station device for transmitting and receiving radio carrier waves will be described which is another example of the radio communication system.
FIG. 13 shows a base station device including a monopole antenna with a skirt which is disclosed by the publication "Antenna Engineering Handbook", page 137, FIGS. 5 and 7 edited by Electrical Communication Society, published by Ohm Co. In FIG. 13, reference numeral 71 designates an antenna radiation element; 19, a coaxial external conductor; 72, a skirt C connected to the external conductor 19; 22, water-proof rings for preventing the entrance of water into the external conductor 19; 73, a coaxial internal conductor; 74, a coaxial connector for connecting a coaxial cable 75; 76, a base station device body; and 50, connecting terminals for signal cables.
The operation of the base station device thus organized will be described.
The length of the antenna radiation element 71 and the skirt C 72 is set to about a quarter (1/4) of the wavelength of a signal employed, so that the skirt C 72, forming a coaxial line with the external conductor 19, is placed in resonance with the frequency of a radio carrier wave which is transmitted or received through the radiation element 71. Hence, when the coaxial cable 75 is connected to the coaxial connector 74, transmission and reception of signals can be achieved through the coaxial cable with the base station device body 76, without being affected by the radio carrier wave. The radiation element 71 and the skirt C 72 form a half-wave dipole antenna, providing an excellent radiation characteristic. Communication signals are transmitted and received with the aid of the connecting terminals 50.
The conventional radio relay system is designed as described above. Therefore, in order to eliminate difficulties that the receiving radio carrier wave and the transmitting radio carrier wave interfere with each other, and the receiving radio carrier wave is suppressed in sensitivity by the transmitting radio carrier wave and noises outside the frequency band including the transmission frequency, it is necessary to space the signal transmitting frequency band and the signal receiving frequency band wide from each other as shown in FIG. 11. Hence, the relationships between the signal receiving frequency band and the signal transmitting frequency band are limited, and according the radio relay device is also limited in function.
With the conventional cordless telephone system as described above, only the slave telephone unit A 37 having the registered ID number can communicate with the master telephone unit 35; that is, the joint use of the master telephone unit 35 is not permitted. In other words, the master telephone unit 35 serves merely as relaying means between the slave telephone unit A 37 and an external telephone set, and there is no method of using the master telephone unit 35 by itself. Thus, the conventional cordless telephone is low in utilization factor. Furthermore, since the master telephone unit 35 is generally installed indoors, use of the slave telephone unit is limited indoors.
The base station device described above suffers from the following difficulties: In the base station device, the antenna is provided, as one unit, in addition to the base station device body 76, and the former is connected through the coaxial cable to the latter. Therefore, the installation is expensive.